1. Field of Invention
The present invention relates to semiconductor technology, and more particularly, to a method for manufacturing a suspended fin and a gate-all-around field effect transistor on a bulk silicon.
2. Description of Prior Art
The integrated circuit industry continues developing according to Moore's law and the feature size of CMOS devices is becoming smaller and smaller. A planar CMOS device on a bulk silicon is facing with severe challenges, such as a short channel effect (SCE), leakage current between the source and the drain, a drain induced barrier lowering effect (DIBL), and the like. To solve the above problems, many novel device structures are proposed, in which a gate structure of the device is changed from the initial single-gate structure to a double-gate structure (i.e. FinFET), a multi-gate structure, or even a surrounding gate which surrounds the channel completely. With an increase of the number of the gate, the gate controllability and the capability of suppressing the short channel effect are enhanced. The above novel device structures, such as a double-gate (FinFET), a multi-gate, or even a gate-all-around device, all involve the fabrication of a channel having a fin structure. Specifically, a suspended fin structure should be fabricated for a gate-all-around device.
Up to now, an SOI substrate is used for manufacturing a gate-all-around device. Since an SOI substrate has a natural buried oxide layer (BOX) which can be used as a sacrificial layer, it facilitates the manufacture of a gate-all-around device. The SOI substrate has the following beneficial effects: easily isolating the devices by a natural buried oxide layer in the SOI substrate, which avoids a latch up effect in a bulk silicon substrate; simplifying the manufacturing process; easily suppressing a parasitic transistor at the bottom; smaller parasitic capacitance; high speed; and good anti-radiation performance. However, there are still many problems in manufacturing a gate-all-around device with an SOI substrate. For example, since the SOI substrate has a self-heating effect and a floating-body effect, complicated source/drain engineering should be introduced into the manufacture process so as to decrease parasitic resistance between the source and the drain.
Since a bulk silicon substrate is still used in a mainstream semiconductor manufacture process at present, researches are focused on forming a gate-all-around device in a bulk silicon substrate, which has important significance in application of a gate-all-around device and the development of the semiconductor industry. To manufacture a gate-all-around device in a bulk silicon substrate, one should first consider how to fabricate a suspended fin structure in a bulk silicon substrate.